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| United States Patent |
6,111,227
|
|
Cress
|
August 29, 2000
|
Furnace exhaust method and apparatus
Abstract
An electrically heated furnace wherein electrical heating elements are
mounted and supported so that they face the inner furnace walls and are
isolated from direct communication with articles being treated within the
furnace such that clean air flows over the heating elements providing
oxygen to create an aluminum oxide coating on the heating elements and
maintains a clean atmosphere about the heating elements. Air circulation
from exterior the furnace is through ports in the furnace walls and over
the electrical heating elements; exhaust from the furnace is through ports
in the furnace walls into a plenum and out through a flue creating
pressure differentials with the pressure in the furnace area where
articles are being subjected to heat is lower than the atmosphere and the
area in which the heating elements are located.
| Inventors:
|
Cress; Steven B. (P.O. Box 30, Glenbrook, NV 89413)
|
| Appl. No.:
|
326198 |
| Filed:
|
June 4, 1999 |
| Current U.S. Class: |
219/400; 373/110; 432/120 |
| Intern'l Class: |
F27D 011/00 |
| Field of Search: |
219/390,391,400
432/120
99/339
373/109,110,118
|
References Cited
U.S. Patent Documents
| 5378144 | Jan., 1995 | Cress | 432/120.
|
| 5674425 | Oct., 1997 | Hong | 219/681.
|
| 5694831 | Dec., 1997 | Haroun et al. | 99/339.
|
| 5756974 | May., 1998 | Hong | 219/681.
|
Primary Examiner: Hoang; Tu Ba
Attorney, Agent or Firm: Schulze; Herbert C.
Parent Case Text
CROSS REFERENCE TO RELATED PATENT APPLICATIONS
The invention is, related to my U.S. Pat. No. 5,378,144 in that it is in
the same broad field as that patent.
Claims
What is claimed is:
1. A method for vitrifying ceramic articles comprising:
providing a heat insulated enclosure including a top, a bottom, and walls;
inserting articles being subjected to heat in said enclosure;
inserting electrical heating elements support means adjacent the walls of
the enclosure;
fastening electrical heating elements composed of material including iron
and aluminum to the support means intermediate the walls and the support
means;
providing first vent means through said walls adjacent said electrical
heating elements for intake of air;
causing air to travel through said first vent means over the electrical
heating elements and over the articles being subjected to heat;
providing second vent means not adjacent the electrical heating elements
for the escape of air from the enclosure;
and, causing air which has traveled over the electrical heating elements
and the ceramic articles to exit the furnace through said second vent
means.
2. The method of claim 1 wherein aluminum oxide coating is caused to be
deposited on the electrical heating elements by reason of oxygen in the
clean air traveling over the electrical heating elements combining with
aluminum in the heating elements.
3. A method for subjecting articles to heat comprising:
constructing a heat insulated enclosure including a top, a bottom, and
walls;
inserting articles to be subjected to heat into said enclosure;
providing electrical heating elements support means adjacent the walls, and
within, the enclosure;
installing electrical heating elements upon the support means intermediate
the walls and the support means; providing first vent means through said
walls adjacent said electrical heating elements for intake of air;
activating said electrical heating elements so as to produce heat, thus
subjecting the article to heat;
causing air to travel through said first vent means over the electrical
heating elements and over the articles being subjected to heat;
providing second vent means not adjacent the electrical heating elements
for the escape of air from the enclosure; and blowing air which has
traveled over the electrical heating elements and the articles being
subjected to heat through said second vent means into a plenum in such
manner that the air in the plenum is at a higher pressure than both the
air pressure in the furnace and the atmosphere pressure outside the
plenum.
4. The method of claim 3 wherein a lower pressure is created in the area of
the furnace where articles are being subjected to heat than the pressure
at the heating elements.
Description
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention is in the general field of electrically heated furnaces and
the like;
The invention is more particularly directed to methods and apparatus
relating to circulation of air and products of combustion in furnaces and
the like;
The invention is most particularly in the field of a new and unique method
of circulating air and exhausting air and the like from furnaces and the
like in a manner which protects electrical heating elements and the like
and which enables a greater uniformity and control of heat within the
furnace.
2. Description of the Prior Art
There have been various attempts to create systems for improved air
circulation and protection of electrical heating elements in electrically
heated furnaces and the like. My invention of the system set forth in my
above referenced U.S. Pat. No. 5,378,144 was a significant advance in the
art.
There continued to be a need for further improvement in the art of
circulation of heated air and the exhaust of contaminated heated air from
furnaces. In particular, it has been deemed desirable to protect
electrical heating elements from physical damage and deterioration due to
physical contact with objects and contamination by the products of
combustion and the like within furnaces and the like. Until my present
invention this has been elusive. Now, however, this is solved with the
system disclosed in this application for patent.
The present invention utilizes a new theory, wherein the heating elements
are reversed to face the insulation in the furnace or the like and input
venting is provided to the area between the heating element plates and the
furnace insulation. This results in many advantages as are explained below
in the summary and in the description of a preferred embodiment.
SUMMARY OF THE INVENTION
In the furnace arts, and particularly high temperature furnaces such as
electrically heated ceramic kilns and the like, a continuing problem is
physical damage to, and deterioration of, the electrical heating elements
by reason of the elements operating in an atmosphere contaminated with
products of combustion and gasses released by products being treated in
such furnaces and by physical damage through contact with various objects
such as in loading and unloading articles from the furnace and from
collapse of kiln furniture.
Until my present invention various air circulation devices have been tried.
For example, my afore mentioned U.S. Pat. No. 5,378,144 was concerned with
this problem, but did not completely solve it.
I have now conceived and developed a new, unique, and effective answer to
this old problem. I have accomplished this by reversing my thinking, and
the thinking of others in this art, as to the disposition of the
electrical heating elements. In the past it been customary to think in
terms of achieving the most direct exposure of articles within a furnace
to the direct radiant heat of the electrical elements. I have now found
that I am able to achieve superior, heating and treatment of articles in a
more economical and timely manner by reversing the electrical heating
elements so that they face the walls of the furnace and the furnace
becomes essentially a convection furnace. By proper arrangement of venting
and exhaust control I achieve extraordinary results, including, among
others: 1) improved heat distribution; 2) clean heating elements ; 3)
protection of heating elements by coating with aluminum oxide; 4)
physically protecting heating elements from damage; 5) reducing air
contamination outside the furnace due to reduced furnace interior pressure
preventing contamination from leaking about the furnace door; 6) reduced
heating cycle time; 7) increased heating element life; 8) uniformity of
temperature and temperature control within the furnace treating interior;
9) cooling the furnace walls and preheating air by fresh air intake
directly over the heating elements.
It is an object of this invention to improve heated air circulation within
furnaces and the like;
Another object is to increase the useful life of heating elements;
Another object of this invention is improve the quality of air adjacent the
exterior of furnaces and the like;
Another object of this invention is to protect heating elements in a
furnace from physical damage;
Another object of this invention is to provide cooling air flow over the
heating elements while at the same time, and by reason of, providing for
automatic production of a protective aluminum oxide coating on the heating
elements, thus reducing heating element deterioration and enhancing
heating element useful life;
Another object of this invention is to cool the furnace interior walls by
introduction of fresh air, at the same time preheating the fresh air;
Another object of this invention is to reduce furnace treatment time
cycles;
Another object of this invention is to enable superior uniformity of
temperature and temperature control within furnaces.
Another object of this invention is to improve the quality of heat
treatment within a furnace.
The foregoing and other objects and advantages of this invention will be
apparent to those skilled in the art upon reading the description of a
preferred embodiment, which follows, in conjunction with a review of the
appended drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a schematic perspective of a furnace of the prior art;
FIG. 2 is a schematic section on 2--2 on FIG. 1;
FIG. 3 is a schematic perspective of an apparatus suitable to practice the
method of this invention;
FIG. 4 is a schematic section on 4--4 on FIG. 3;
FIG. 5 is a schematic section on 5--5 on FIG. 3; and
FIG. 6 is a schematic diagram illustrating pressure zones in and around a
furnace of this invention.
DESCRIPTION OF A PREFERRED EMBODIMENT
An inventory of items bearing reference numerals on the accompanying
drawings:
______________________________________
Item Description
______________________________________
10 prior art furnace
12 firebrick
14 door
15 hinge
16 heating elements
17 heating element backing/support
18 articles being treated in oven
20 exhaust duct
24 exhaust
30 contaminated air
40 contaminated air
100 furnace
114 door
115 hinge
116 heating elements
117 heating element backing/support
120 seal
121 exhaust ports
122 plenum
123 check valves
124 exhaust stack
125 air intake port
126 check valve
127 fan
128 fan
130 cold air intake path
135 heated air path
140 contaminated air path
201 atmosphere outside furnace
202 zone between furnace wall and heating
elements
203 furnace area in which articles are treated
204 plnum
205 kaowool
______________________________________
FIGS. 1 and 2 show schematically a high temperature furnace and the air
flow through the furnace according to the art prior to my present
invention. A furnace 10, shown here as a cube, is formed with insulated
walls 12, an insulated door 14, and an exhaust stack 24 for exhaust
gasses. In operation there will be articles 18 within the furnace, which
articles are subjected to heating in the furnace. Electrical heating
elements 16 will be mounted on a backing and support member 17. The
electrical heating elements 16 face the articles being subjected to heat.
Contaminated heated air 40 containing various corrosive impurities will
circulate throughout the furnace and in contact with all surfaces
including the electrical heating elements as is known to those skilled in
the art. The contaminated air coats the heating elements with impurities
and causes corrosion and ultimate failure of the heating elements.
In some cases the heating elements may be somewhat enclosed and partially
protected by insulation such as cement or the like. This is not thoroughly
effective. While there may be a measure of passive protection by doing
this it is never complete protection since the insulation will crack and
allow the contaminated air to work its destruction of the elements.
The heated air may be exhausted through duct 20 and chimney 24.
FIGS. 3, 4, and 5 illustrate, schematically, my new invention. FIG. 3
appears to be a customary furnace 100 with door 114 and exhaust stack 124.
A feature which is unusual in FIG. 3 shows a plenum chamber 122. From its
outer appearance my new furnace may not seem unusual, but the unusual
nature in operation will be understood by those skilled in the art upon
reading this complete specification.
Upon examining FIGS. 4 and 5 the unusual nature of furnace 100 will become
immediately apparent to those skilled in the art. It is observed that the
furnace 100 has walls of firebrick or the like 112, an insulated door 114,
electrical heating elements 116, and heating element support and backing
member 117. Work pieces 118 such as ceramic goods or the like are being
treated within the furnace. It is important to note that the electrical
heating elements do not face the work pieces 118, but they face the walls
112 of the furnace. There is a small space between the walls and the
heating elements sufficient to allow adequate air flow.
One feature of this method and apparatus is that the loading of the work
pieces is now safe. Before my present invention, when loading work pieces,
especially where a very full load is to be inserted in a furnace, damage
can be done to the heating elements by inadvertent scraping or bumping of
a work piece against the elements. Additionally, loads in the furnace are
usually supported on kiln fixtures which can, and do, collapse from time
to time. When this occurs severe damage can be done to the heating
elements. As is clear from an examination of the drawings and from the
general knowledge of those skilled in the art the collapse of a load in my
new furnace will not affect the heating elements, nor will scraping or
other contact when inserting and removing loads.
A number of ports 125 are provided through the walls of the furnace. Ports
125 allow cool air 130 to enter the furnace. Each port may be equipped
with a check valve such as a bellows type flap covering 126 or the like on
the inside of the ports 125. These check valves prevent air from exiting
the ports 125 but allow air from outside to enter as will be known by
those skilled in the art. The air being introduced into the furnace in
this manner cools the furnace walls and at the same time becomes
preheated. The preheated clean air then flows over and about the heating
elements. This aids in the protection of the heating elements by keeping
them clean, while at the same time forming an aluminum oxide coating on
the heating elements as discussed below.
Exhaust ports 121 with or without check valves 123 allow the exhaust of
heated and contaminated air from the interior of the furnace. If check
valves 123 are used they allow exhaust air to enter plenum chamber 122
from which it passes through flue 124 to the atmosphere or to a treating
chamber for removal of contaminates as is known to those skilled in the
art. The check valves 123 will prevent exhaust air from reentering the
furnace.
Fan(s) 127 and/or 128 may be used to enhance the air flow out of the
furnace as will be understood by those skilled in the art.
The heating elements are primarily composed of iron, with a very small
percentage of aluminum. In the operation of my new system, oxygen from the
clean air circulating over the elements--isolated from the contaminated
air in the furnace--will gradually cause oxidation, thus coating the
elements with aluminum oxide, which further protects the elements, as will
be understood by those skilled in the art.
As will be understood by those skilled in the art, atmospheric air 130 will
enter the furnace through ports 125 and, if used, check valves 126. This
air will be heated by the heating elements 116 and will enter the furnace
treating area 133 as heated air 135. At this time the air 135 will begin
to contact the work pieces 118 and become contaminated air 140, which is
finally exhausted through ports 121 into plenum chamber 122 and then to
exhaust flue 124 for release to the atmosphere or treatment as previously
mentioned.
In my new system, there will be essentially four different pressure zones
as shown schematically in FIG. 6. The first pressure zone is the
atmosphere 201 outside the furnace. The next pressure zone, which is the
zone 202 between the heating elements and the wall of the furnace, will be
slightly lower pressure than the atmosphere zone 201. The portion of the
furnace, zone 203, in which articles are treated, will be at a lower
pressure than zone 202, thus keeping the contaminated air from entering
zone 202. Zone 204, within the plenum, will be the highest pressure, as
will be understood by those skilled in the art. This higher pressure will
be the greatest when it is created by the action of the fan(s) 127 and/or
128 (not shown in FIG. 6, but understood by those skilled in the art and
by reference to FIG. 4).
As an added optional feature to further protect the heating elements in
FIG. 6 from contamination and deterioration by reason of contact with
contaminated air, I have shown loosely packed kaowool or like 205 between
the ends of each bank of heating elements and the adjacent furnace wall.
The kaowool will allow the passage of clean air, but will entrap the heavy
molecules of impurities in the unlikely event that there should be some
backflow of contaminated air from zone 203 to zones 202
During this whole process no contaminated air has been able to come in
contact with the heating elements, leaving them clean and not corroded. At
the same time, the protective coating of aluminum oxide is being formed on
the elements as previously described.
In customary furnaces before this invention, the heating of articles being
treated in the furnace has not been totally uniform. The direct radiant
heat from the electrical heating elements is not uniform, as is known to
those skilled in the art. Operating in accordance with this new invention,
the air is heated at a distance from the articles being treated. As this
heated air flows into the area in which articles are treated, the articles
receive uniform heat since the air has achieved a stabilized heat
condition not affected in the portion of the furnace in which articles are
treated by the irregular influence of the radiant heat.
While the embodiments of this invention shown and described are fully
capable of achieving the objects and advantages desired, it is to be
understood that such embodiments have been presented for purposes of
illustration only and not for purposes of limitation.
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